This invention relates to fuel cell systems and, more particularly, to multi-stack fuel cell systems.
In building fuel-cell systems, the fuel cells are conventionally stacked one on the other to form a fuel-cell stack. The number of cells determines the power rating of the stack and to provide systems with higher power ratings, a number of fuel-cell stacks are utilized and the outputs of the fuel cell stacks combined to provide the desired power output.
In one type of a multi-stack fuel cell system, a modular multi-stack fuel cell assembly includes a plurality of fuel cell stacks housed within a rectangular or box-like enclosure and arranged in line along the length of the enclosure. Each of the stacks within the enclosure has inlet manifolds for receiving the fuel and oxidant gas needed to operate the stack and outlet manifolds for outputting exhaust fuel and oxidant gases from the stack. The enclosure includes fuel and oxidant gas inlet ports for communicating through piping or conduits with the respective fuel and oxidant gas inlet manifolds of the stacks, and fuel and oxidant gas outlet ports for communicating through piping with the oxidant and fuel gas outlet manifolds.
In such system, in order to insure an appropriate uniform flow distribution and a desired pressure differential through the stacks, flow baffles are provided in the piping or conduits connecting the fuel and oxidant gas inlet ports to the respective stack inlet manifolds. Each of the stacks and the piping within the enclosure are also insulated to thermally isolate the stacks from the enclosure. The cold box-like design of the enclosure requires thermal expansion joints inside as well as outside of the enclosure to minimize the pressure differential across the fuel and oxidant seals. Nitrogen is also provided to purge any minute leaks from the fuel cell stacks into the enclosure.
While modular multi-stack fuel cell assemblies of the above type performed as desired, the piping and baffle requirements made each assembly complex and expensive. The thermal insulation requirements were also stringent, further adding to the cost of each assembly. Additionally, the need for a nitrogen gas purge added another gas stream increasing the process control requirements. These factors have lead designers to look for less complex and less costly design alternatives.
U.S. Pat. No. 7,323,270, assigned to the same assignee herein, describes an improved modular multi-stack fuel-cell assembly, in which stack flow distribution and differential pressure requirements are realized in a simpler and more cost effective manner, and in which input and output port and piping requirements are significantly reduced. The '270 patent discloses a modular multi-stack fuel cell assembly in which the stacks are situated within an enclosure or a containment structure and which includes a gas distributor within the structure for distributing received fuel gas to the stacks and for receiving exhausted fuel and oxidant gases from the stacks. The gas distributor is disposed symmetrically and centrally of the fuel cell stacks within the structure so as to promote desired uniform gas flow and uniform pressure differential through the stacks. The distributor in the '270 patent includes a first section for distributing received fuel to manifolds of each of the fuel cell stacks through equal length conduits, a second section for receiving exhausted fuel gas from each of the stacks through equal length conduits and a third section for receiving exhausted oxidant gas from each of the stacks through equal length conduits.
It is desired to provide a more advanced modular multi-stack assembly for improved reliability and greater accessibility and serviceability so as to reduce the manufacturing and maintenance costs of the assembly, extend the life of the assembly and to improve its performance. It is also desired to provide an improved modular multi-stack assembly with a space-saving design that allows use of anode exhaust gas within the assembly to generate oxidant gas for use in fuel cell cathode compartments.
It is therefore an object of the present invention to provide a further simplified modular multi-stack assembly in which oxidant gas is supplied to an oxidant inlet face of each fuel cell stack through an oxidizer assembly within the modular assembly.
It is a further object of the invention to provide a modular multi-stack assembly which includes at least one oxidizer unit within the enclosure adapted to receive anode exhaust and input oxidant gas and to output oxidant gas for use in the cathode side of the stacks.
It is also an object of the present invention to provide a modular multi-stack assembly in which a plurality of sealed regions are formed within its enclosure for improved gas separation and distribution within the assembly.